Electromagnetic telephone relay



Feb. 13, 1968 K. A. LUNDKVIST ELECTROMAGNETIC TELEPHONE RELAY Filed Jan.6. 1966 INVENTOR.

\(nm. Ann. Lumonvlgr United States Patent 3,369,206 ELECTROMAGNETICTELEPHONE RELAY Karl Axel Lundkvist, Stockholm, Sweden, assignor toTelefonaktiebolaget L. M. Ericsson, Stockholm,

Sweden a corporation of Sweden F lled Jan. 6, 1966, Ser. No. 519,058Claims priority, application Sweden, Mar. 10, 1965,

3,151/65 5 Claims. (Cl. 335273 ABSTRACT OF THE DISCLOSURE Anelectromagnetic relay the core of which is rotatable in the coil of therelay and has at its end facing a pivotal armature of the relay anon-axial or set-oflf portion so shaped that the distance between thepivot axis of the armature and the principal area of a magneticattraction of said non-axial core portion varies in accordance with theangular position of the core in the coil whereby the relay can be set inaccordance with the contact assembly to be controlled by the relaywithout altering the working angle of the armature and the extent oflifting or lowering of the contact assembly.

In automatic telephone establishments electromagnetic relays of standarddesign are used. They generally consist of an angular-bent yoke, onwhich contact spring assemblies, an armature with a residual plate andan iron core with a coil are fastened. The yoke constitutes the frame ofthe relay and is maintained unchanged independently of the purpose ofthe relays while the number of contact spring assemblies and the numberof contact springs in each assembly are changed within wide limitsdependent on the use of the relay. The winding of the coil also variesvery much both with regard to electric data and with regard to volume.The residual plate of the armature is likewise changed dependent on theuse of the relay. The length of the contact springs, contact distance,contact pressure and the lifting of the movable contact springs areaccurately determined magnitudes that are not changed as they have beendetermined according to a very comprehensive practical and theoreticalwork. The contact spring assemblies, the yoke and the armature have beenthe unchangeable standard details of the telephone relay while the ironcore, the coil and the residual plate are details that are changedpartly with the number of contact springs, partly to adapt theproperties of the relay to its use.

A standard relay must in weight and volume be diphone relay are thediameter of the winding wire in the coil and the thickness of theresidual plate and also the diameter of the iron core. Sometimes alsothe diameter of the end of the iron core at the air gap is varied. Tovary the winding according to the load of the relay and according to theresistance of the operating circuit is a necessary and natural measurewhile on the other hand a variation of the dimensions and the appearanceof the iron core must be regarded as a deviation from thestandardization. Alteration of the thickness of the residual plate mayappear acceptable in view of the insignificant size and cost of thedetail. In reality also the variation of the residual plate is notdesirable as the length of the iron core and the length of the yoke donot coincide at more than one thickness of the residual plate. Thearmature travel of the relay is likewise changed with the residual plateand increased demands on adjustment possibility for the armature traveland for the lifting of the contact spring assemblies become a necessaryconsequence.

It has been proposed to construct a telephone relay so, that the lengthof the lever of the spring load on the armature may be varied. Then thearmature travel must be simultaneously varied in order that the movementof the contacts should not be changed. The proposal implies manyconstructive difiiculties and therefore it has not taken practicalshape.

The present invention has for a purpose to reduce in an electromagneticstandard relay with from case to case varying load and workingconditions, the need of iron in the magnetic circuit and the need ofcopper in the relay winding and to bring about with simple means areadjustment of the relation between the levers of the relay armature inview of the intended load.

This is achieved by means of a side-position of the end of the iron coreof the coil at the air gap after which by turning the end of the ironcore the distance between the working point of the magnetic field on thearmature and the axis of rotation of the armature is changed inproportion to the magnitude of the load without change of the angle ofrotation of the armature and the lifting of the contact springs.

In order to explain the invention it is assumed that a telephone relayis loaded with that maximum number of contact springs for which therelay is intended and is held in released position and that the relaywinding is traversed by a current that produces a magnetic fieldsufficient for the operation of the relay. When the relay armaturereleases, it will be attracted against the end of the iron core. Herebyfirst a number of easily stretched contact springs, so-calledunder-springs, are actuated which are lifted and make contact withharder stretched contact springs which are to give the contact pressure,and when the armature is a few tenths of a millimetre from the end ofthe core the armature will pass its critical position, whereby the totalcontact spring load shall be overcome. Then the spring load risesinsignificantly during the last part of the movement of the armaturewhile the magnetic flux increases rapidly and therefore the magneticflux density in the iron circuit can at least in some part have a chanceto approach saturation already when the critical position is reached. Ifregard is paid to reasonable margins for the operation of the relay bothregarding the magnitude of the tractive force and regarding thesaturation in the iron, it is possible to determine the cross sectionarea of the iron, the remaining movement of the armature in the criticalposition and the levers of the armature in such a way that an optimumin' respect to weight and volume for the relay is achieved. The magneticflux density in the end of the core at the air gap is here indicated byB, the area of the iron core at the core end by A, the magneticresistance disregarding the remaining movement of the armature in theair gap by m. The spring load is called P, its lifting is called 0 andits lever in relation to the centre of rotation of the armature isindicated by b. The magnetic field at the end of the core becomes B A,its lever on the relay armature is indicated by a, and the remainingmovement of the armature in the air gap at the critical position isindicated by d. The cross section of the iron core is assumed to be acircular surface as a round coil gives the smallest copper consumption.The

number of ampere turns required for the operation is indicated by M. Dueto the leakage between the iron core and the yoke the magnetic fluxdensity will be greater in the iron core than at the end of the core.The relation between the maximum value of the flux density within theiron core and B is supposed to be a number k valid for critical positionof the armature and determined empirically.

If the dispersion of the field in the air gap is neglected, therelations (1), (2) and (3) below are valid. The Equation 1 indicatesequilibrium between the moment of the load and of the field on thearmature. The Equation 2 indicates the relation between the flux densityB and the number of ampere turns. The Equation 3 indicates a meregeometrical relation.

e the absolute permeability for vacuum.

In the above equations are P and determined by the construction of thecontact spring assemblies. The maximum fiux density k.B is determined bythe properties of the iron. The number k varies somewhat with the airgap d. The value In is composed by the thickness of the residual plate,the magnetic resistance of the iron and by the magnetic resistance isconsequence of the surface treatment of the yoke, of the armature and ofthe iron core.

In a finished relay one cannot alter A, nor can b be altered as has beenmentionad above. If the lever b is supposed to be determined there willbe obtained out of (1), in case the relay is loaded with a maximumnumber of contact springs, the relations:

2 .,-P b 2 (4) When the load P decreases, also the lever a and thus theair gap d can be decreased. The value m is determined in practice by theremanence of the iron and by the surface treatment and may here beregarded as a value given in advance, which cannot be varied.

In normal telephone relays both A and a and b are fixed, unchangeablemagnitudes. According to Equation 2 the required number of ampere turnsM can then be reduced only by a decrease of B, i.e. that the iron volumeis utilized completely only at maximum load. On decreasing the load Pthe need of ampere turns is not diminished in proportion to P but onlyin the proportion VF. Out of (2) and (4) is namely obtained:

Thus the relay becomes less sensitive at low load when often greatersensitivity is desirable.

From (4) is seen that an increase of a allows the decrease of A, i.e.reduces the need of iron in the relay. When the iron core of the relaycoil can be made thinner also the need of copper in the windingdecreases at a definite number of ampere turns. From (5) is seen thatthe increase in M owing to an increased a will be relatively small andcan be completely avoided if m can be reduced for example by thinnerresidual plates.

On an estimation of the dimensions of a relay it is necessary to proceedfrom an average value for the load and from this determine partly thecross section of the air gap and of the iron circuit, partly the leversa and b of the armature and also the length of the yoke and of the coil.The iron core in the coil is in this connection of course made straightwithout a side-position of the end of the core at the air gap.

At heavier loads the cross section of the iron becomes insufficient ifthe length of the lever a is maintained unchanged. According to theinvention the end of the iron core is therefore shaped so, that thelever a may be varied upwards and downwards around the average valuethat corresponds to the lever a at a straight iron core. At a smallvalue on a the relay armature becomes short and light. This is of valuein sensitive relays which should be rapid in spite of only small forcesbeing at disposal.

At decreased load only a smaller number of ampere turns is required andthe iron circuit becomes utilized unsatisfactorily if the levers a and band the area A are left unchanged. According to the invention anincreased sensitivity is obtained in weakly loaded relays by decreasingthe lever a.

In slow-operating relays a large magnetic field is desired but also alow resistance in the copper tube that produces the slow-operation isrequired. These factors counteract each other at each change of thediameter of the relay core. An increase of the lever a causes howeveralways a better holding and consequently a more eifective slow-operationand therefore the invention comes into use also in slow-operatingrelays.

At low loads, especially relays with only two contact springs, a greatsensitivity is often required, i.e. that the necessary effect on thewinding upon operation should be small. If the lever a is decreased byplacing the end of the core aside according to the invention, the airgap Will decrease. By increasing the area A of the air gap the flux isincreased furthermore and the sensitivity of the relay increases. Theflux density B in the air gap will be high in spite of the decreasing ofthe number of ampere turns. The stray fields may be supposed to decreasewith the number of ampere turns. The relative change of the magnitude ofthe load from average load to low load becomes considerably greater thanfrom average load to maximum load.

On a relay intended for standardization a residual plate of definitethickness is desired as the length of the relay core has to be adaptedto the length of the yoke and the armature cannot lie on the level ofthe end of the relay core for more than one determined value onthe-thickness of the residual plate. If the thickness of the residualplate is determined for a relay loaded with the average number ofcontact springs, this residual plate can be maintained at all otherloads, if the lever a is varied. An adjustment of a implies a levellingbetween the operation margin of the relay and its release margin. Thusit is suitable that this adjustment may be made continuously and notonly step-by-step. The invention may in view of the adjustment of therelay come in to use also for relays with a contact spring loadcorresponding to the average load.

In the accompanying drawing several preferred embodiments of theinvention are shown by way of illustration and not by way of limitation.

In the drawing:

FIG. 1 is a diagrammatic view, partly in section, of a relay set for aheavy load to be controlled;

FIG. 2 is a similar view of the relay but set for a light load to becontrolled; and

FIG. 3 is a perspective fragmentary view of a modification of the relay.

In the relay according to FIGS. 1 and 2, a magnetic circuit is formed bythe yoke 1, the armature 2 and the iron core 3. A coil 4 is located onthe iron core 3 which is turnable in the coil, and a contact springassembly 5 is mounted on the yoke 1.. The end of the iron core 3 in theair gap is bent to the one side. In FIG. 1 the iron core is turned sothat the distance between the end of the core and the yoke 1 is as greatas possible. In FIG. 2 the iron core is turned compared with FIG. 1 sothat the end of the core is as near to the yoke as possible. Allintermediate positions are readily conceivable. Moreover, the end of thecore does not need to lie symmetrically in relation to the armature 2.The iron core 3 is potted in a plastic such as Bakelite, so that two endplates 9 are formed and the iron core is insulated from the coil 4. Inthis way the bent end of the iron core is located inside the fore endplate, so that no extension of the core or loss of coil space arises. Asthe level of the end of the core runs obliquely to the axis of the bentcore part the surface of the end of the core can be made larger than thecross section of the iron core. Dependent on the bending angle of theiron core the size of the pole face may be varied so, that a relay thatis effective at all loads is obtained.

The end of the core can also be formed by staving or be be provided witha loose pole piece that can be turned around the iron core of the coilwithout a simultaneous rotation of the coil itself.

In FIG. 3 is shown a round iron core 8, the end of which has been shapedto an adequate form such as a radial arm 8a. The coil 4 is wound on aloose bobbin and the iron core is extended through the bobbin with thecore end 8a protruding therefrom. The back end plate 6 of the bobbin isshaped to carry terminals 7 for connecting the ends and connections ofthe coil to the bobbin. The iron core can be turned without the coilbeing turned. The armature and the contact spring assemblies are omittedin order to simplify the figure.

I claim:

1. An electromagnetic relay comprising in combination: a yoke, arotatably supported elongate core having a nonaxial end portion, a coilencompassing the core permitting rotation thereof, and an armaturepivotally mounted adjacent to said nonaxial end portion of the core, thepivot axis of the armature being disposed laterally of said nonaxialcore portion, said yoke, core and armature constituting a magneticcircuit including an air gap defined by the armature and the nonaxialend portion, the width of said air gap corresponding to the pivotalposition of the armature in reference to the nonaxial end portion of thecore, whereby the leverage of the magnetic force attracting the armaturetoward said nonaxial core portion varies in accordance with the distancebetween said core portion and the pivot axis of the armature, saiddistance being a function of the rotational position of the core in thecoil; and

a movable load means coacting with the armature to bias the same intothe direction away from said nonaxial core portion and to be displacedby the movement of the armature toward and away from said core portion.

2. An electromagnetic relay according to claim 1 Wherein the tip of saidnonaxial end portion of the core is located in one plane in all angularpositions of the core in the coil whereby the angle of the pivotalmovement of the armature and thus the displacement of the load means arethe same for all rotational positions of the core.

3. An electromagnetic relay according to claim 1, Wherein said core is astraight core and said nonaxial end portion of the core is a portionbent-off in reference to the center axis of the core.

4. An electromagnetic relay according to claim 3, Wherein the tip ofsaid nonaxial end portion of the core is at a slant in reference to thecenter axis of the bent-01f core portion, the plane of said slant beingnormal to the center axis of the straight core portion.

5. An electromagnetic relay according to claim 1, wherein said core is astraight core and said nonaxial end portion of the core is in the formof an arm substantially radially extending from the straight coreportion.

References Cited UNITED STATES PATENTS 2,076,658 4/1937 Morgenstern33528l X 2,294,327 8/1942 Zupa 335281 X 2,588,534 3/1952 Jorgensen335132 BERNARD A. GILHEANY, Primary Examiner.

G. HARRIS, Assistant Examiner.

